1. Field of the Invention
The present invention relates to a metal oxide paste composition comprising a carboxylic ester dispersant or a phosphate dispersant, and a method for manufacturing a semiconductor electrode using the same. More particularly, it relates to a metal oxide paste composition having excellent dispersibility, which comprises a carboxylic ester dispersant or phosphate dispersant having a tail structure of hydrophilic or hydrophobic blocks, as well as a method for manufacturing a semiconductor electrode using the same.
2. Description of the Prior Art
Solar cells, which are photoelectric conversion elements that convert solar light into electricity, are sustainable and eco-friendly, unlike other energy sources, and thus are of increasing importance. In an early stage of development, monocrystalline or polycrystalline silicon solar cells were mainly used. However, silicon solar cells require large-sized expensive systems and equipment to manufacture them, are manufactured at high cost due to high raw material costs, and are limited with respect to the efficiency with which they convert solar energy into electrical energy. For this reason, a new alternative has been studied.
As an alternative to the silicon solar cells, attention is being concentrated on organic material-based solar cells that can be manufactured at low cost. Particularly, dye-sensitized solar cells having low manufacturing costs are receiving much attention.
The dye-sensitized solar cell is a photoelectrochemical solar cell comprising a semiconductor electrode having metal oxide nanoparticles adsorbed thereon, a counter-electrode, and a redox electrode disposed in the space between the two electrodes.
The photoelectric efficiency of the dye-sensitized solar cell depends on the amount of dye adsorbed on the surface of a metal oxide layer. Because the dye adsorbed on the surface of the metal oxide layer absorbs light with a high efficiency when it is present as a monomolecular layer, the absorption of solar light increases as the surface area of metal oxide having dye molecules adsorbed thereon increases. Thus, in order to obtain a high-efficiency solar cell, it is necessary to maximize the surface area of a metal oxide semiconductor film, such that it can have a maximum amount of the dye adsorbed thereon.
Accordingly, nanocrystalline materials having many anchoring sites capable of adsorbing dye particles can be used. However, because the nanocrystalline materials have high surface free energy, the metal oxide nanoparticles may show a strong tendency to cohere to each other. If the metal oxide nanoparticles cohere to each other in this way, the packing density achieved when forming the light-absorbing layer of a solar cell will be reduced, and thus the photoelectric efficiency of the resulting solar cell will also be reduced.
In an attempt to solve this problem, Japanese Patent Laid-Open Publication No. 2002-50413 discloses a technique for forming a photosemiconductor layer, comprising mixing photosemiconductor powder with a surfactant and a dispersant, such as polyethylene glycol, polyvinyl alcohol, hydroxypropyl cellulose, polyvinyl pyrrolidone or polyacrylic acid, calcining and pulverizing the mixture to prepare porous photosemiconductor particles, and mixing the prepared porous photosemiconductor particles with conventional photosemiconductor particles.
However, the dispersant disclosed in the above prior art cannot provide sufficient dispersion of the metal oxide, and thus is limited in that it cannot sufficiently improve the photoelectric efficiency of a solar cell manufactured using the same.